There exist numerous, known conditions which may occur on either human or non-human animal skin that may be expressed as elevations, patches or other types of disfigurement in or on the skin. Some of these conditions are quite contagious and medically troublesome. However, all are cosmetically unacceptable for obvious reasons. Dermal conditions falling within these categories include warts, skin tags, seborrhea keratoses, dermal eruptions caused by papilloma virus, etc.
Effective and safe methods for the treatment of such conditions have long been desired. Some methods and compositions are known to treat such dermal abnormalities, and such compositions may be sold over the counter for direct application to the skin by the patient or are produced for administration solely by physicians.
The most common of the known methods is the treatment of the dermal lesion with an acidic or keratolytic agent. Many of these products are available "over the counter" for application by the patient. Such compositions and methods generally include the use of salicylic acid which has been approved for use in over the counter products by the United States Food and Drug Administration. However, other acids suitable for the treatment of dermal lesions are also known.
For example, U.S. Pat. No. 4,224,339 discloses the use of a composition comprising cysteic acid, homocysteic acid, cysteine sulfinic acid and chelates of these compounds and metallic compounds to treat warts. Other methods employing acidic agents are disclosed in U.S. Pat. Nos. 4,778,786, which is directed to the use of a composition comprising hydroxybenzoic acid; 5,045,559, which is directed to the use of a composition comprising pyroglutamic acid; and 5,001,156, which discloses the use of a composition comprising lipophilic quaternary ammonium salicylate to treat various keratoses. Also, British Patent No. 2,202,441 discloses the topical application of composition comprising citric acid in dimethylsulfoxide to treat warts.
The acidic agents discussed above are used for their keratolytic effect on the lesion. It is believed that the acidic agent acts to dissolve the intercellular matrix in the lesion, causing it to slough off of the skin. With continued and careful treatment, these acidic agents have been found to be generally effective in treating dermal lesions. However, such agents also have shown disadvantages in that they require multiple treatments in order to completely remove the lesion. If the patient does not strictly comply with the multiple treatment regimen, the lesion will frequently repair itself and reappear.
Other known methods for treating skin lesions comprise the application of cryogenic agents to the lesions, a process known as cryotherapy. Unlike acids which act by dissolving the intercellular adhesion within the lesion, it is believed that cryogenic agents act to freeze the water in the tissue of the lesion, thus lysing the cells upon warming. This lysing action effectively kills the cells which are then sloughed off the body as dead tissue.
Cryotherapy is generally practiced only by physicians and cryogenic agents are not available "over the counter." Current cryogenic agents available to the physician utilize liquified gases (such as liquid nitrogen) or fluorinated hydrocarbons (such as FREON.RTM.). An example of the use of cryogenic material is disclosed in German Offenlegungsschrift 2 302 005, which is directed to a wart-removing composition which comprises a hydrocarbon or halogenated hydrocarbon coolant, an antibacterial agent and an anti-inflammatory agent. The coolant disclosed for use in the patented composition is difluorodichloromethane. The use of various refrigerants, such as dimethyl ether, alone for the treatment of the skin of a human or animal is disclosed in U.S. Pat. No. 4,865,028.
Although known cryogenic agents reach temperatures effective for cryotherapy, such agents have also demonstrated numerous practical disadvantages. For example, liquid nitrogen readily evaporates and thus requires special storage. Fluorinated hydrocarbons, although effective as cryogenic agents, are known to be deleterious to the environment, particularly the ozone layer. Moreover, most of the known cryogenic agents are chemically and/or physically incompatible with acidic agents, such as salicylic acid. Thus, combinations of these materials have heretofore not been used.
Other known methods for treating skin lesions include procedures to surgically remove the infected tissue. This may be accomplished by simply cutting the tissue with a scalpel or may involve more modern techniques, such as cauterization of the lesion as taught in British Patent No. 1,537,235. Other methods of treatment encompassing surgical procedures include laser treatment, as discussed in French Patent No. 2 258 872, and vacuum treatment, as discussed in German Patent No. 3 341 881. Although effective in removing the treated lesion, such methods are disadvantageous as they cause scarring at the point of surgery.
Also, more recently, other methods for treating skin lesions have become known which comprise the use of pharmaceuticals and chemical agents other than acids, which have heretofore not been used to remove skin lesions. For example, U.S. Pat. No. 4,866,095 discloses the use of adducts of 1,8-dihydroxy-anthrone to treat psoriasis or warts. U.S. Pat. No. 5,017,587 is directed to the use of cycloheximide to heal plantar warts. U.S. Pat. No. 4,711,904 discloses the use of dimethyl isosorbide to treat skin disorders. Antiviral agents have also been proposed for the treatment of warts as disclosed, e.g., in European Patent No. 3 027 758. However, the efficacy of such treatment methods remains in question.
Accordingly, although methods exist which have been relatively effective in treating dermal lesions of humans or animals, each of the known methods has certain disadvantages. Thus, it can be seen that there exists a need for compositions useful for treating lesions on the skin of humans or animals and methods for their use which are efficacious, safe and practical.